5,Doppler Principle: Doppler theory based on time, when radio waves encounter an object in the moving process will be reflected when the waves, the frequency of the reflected wave will hit the object with the movement to change state. If the radio waves encounter an object position is fixed, then the reflected wave frequency and transmitting frequency waves should be equal. If the object moves toward the launch, then the reflected waves will be compressed, that will increase the frequency of the reflected wave; otherwise the reflected wave's frequency decreases.